This invention relates generally to gas turbine engines, and more specifically to variable stator vane assemblies used with gas turbine engines.
At least some known gas turbine engines include a core engine having, in serial flow arrangement, a fan assembly and a high pressure compressor which compress airflow entering the engine, a combustor which burns a mixture of fuel and air, and low and high pressure turbines which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. At least some known rotor assemblies, such as a high pressure compressors, include a plurality of rows of circumferentially spaced rotor blades, wherein adjacent rows of rotor blades are separated by rows of variable stator vane (VSV) assemblies. More specifically, a plurality of variable stator vane assemblies are secured to casing extending around the rotor assembly and wherein each row of VSV assemblies includes a plurality of circumferentially-spaced variable vanes. The orientation of each row of vanes relative to the rotor blades is variable to control air flow through the rotor assembly.
At least one known variable stator vane assembly includes a trunnion bushing that is partially positioned around a portion of a variable vane so that the variable vane extends through the trunnion bushing. Each variable vane is coupled radially between the casing and the inner shroud such that the trunnion bushing extends between the casing and a radially outer spindle extending from the vane, and such that an inner bushing extends between the inner shroud and a radially inner spindle extending from the vane. More specifically, and with respect to the radially inner side of the variable vane, the inner shroud is retained to the VSV's by a plurality cylindrical pins extending through a respective hole formed in the inner shroud and into a matching cylindrical groove formed along the radial inner spindle and the inner bushing. Accordingly, only line-to-line contact is established between each pin and each vane, and as such, to prevent the inner shroud form rotating with respect to the variable vanes coupled thereto, two pins must be used per shroud.
Over time, because only line-to-line sealing is defined between each pin and each variable vane, wear between the pins and variable vanes may cause possible gas leakage paths to develop within the VSV assembly. Such leakage may result in failure of the bushing due to oxidation and erosion caused by high velocity high temperature air. Furthermore, once the bushing fails, an increase in leakage past the variable vane occurs, which results in a corresponding rotor performance loss. In addition, the loss of the bushing allows contact between the vane and the casing and/or inner shroud which may cause wear and increase the engine overhaul costs.